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<html>
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		<title>递归，预编译（下）</title>
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		<script type="text/javascript">
			/* Undefined,null,NaN不直接等于真假------[],””,0可以直接==false */
			/*Undefined,null,NaN其中 (+null) 运算是0 其他NaN*/
			/* (+Undefined)====nan */
			if(1+null){document.write((+null)+'--'+(+NaN)+'--'+(+"")+'--'+(+undefined))}
			
		document.write('----练习题：(window.foo||(window.foo=“asc”))=='+(window.foo||(window.foo='asc')))
		
		
		</script>
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